The present invention relates to internal combustion engines; more particularly, to engine cam phasers for controlling the phase relationship between an engine""s camshaft and crankshaft; and most particularly, to a hydraulic seal assembly between fixed and rotatable elements of a cam phaser assembly.
Cam phasers for internal combustion engines are well known. A cam phaser operates between the engine""s cam timing chain or belt and a camshaft to alter the phase relationship between the camshaft and the crankshaft, thereby varying the timing relationship between the pistons"" cycle and the valves"" cycle on demand from an engine control module (ECM).
In a vane-type cam phaser, the phaser comprises an outer portion, known in the art as a stator, that is driven from the crankshaft by a camshaft timing chain, and an inner portion, known in the art as a rotor, that is fixedly connected to the camshaft and is rotatable through a limited central angle within the stator. The rotor and stator rotate together when the engine is running. The rotor includes outwardly-extending radial lobes which interleave with inwardly-extending radial lobes of the stator to form hydraulic timing-advance and timing-retard chambers therebetween. Controllably admitting hydraulic fluid, such as oil from the front bearing of the camshaft, to the chambers via an oil control valve (OCV) serves to change the phase angle between the rotor and stator and thus the phase angle between the crankshaft and the camshaft.
In a spline-type cam phaser, the rotor and stator are related by a piston having mating reverse-handed helical splines therebetween, the piston being hydraulically driven axially to change the relative phase of the rotor and the stator. This type of cam phaser is also actuated via an. OCV and pressurized oil supply.
Typically in the prior art, a cam phaser assembly is bolted to the end of the camshaft by a central bolt and is shrouded by a timing-chain cover bolted to the engine and thus stationary. In installations wherein only minimal engine adaptation is permitted, the OCV is mounted on the timing-chain cover. To reach the OCV, pressurized oil from the camshaft bearing passes longitudinally through the bolt, exiting through a passage in the bolt head, and then passes through a passage in the timing-chain cover and into the OCV. From the OCV, oil is selectively supplied to the cam phaser chambers via phase-advance and phase-retard passages in the timing-chain cover, in the phaser, and in the bolt.
A first problem exists in supplying oil from the stationary passages in the timing-chain cover to the rotating passages in the phaser. Even very small eccentricities in the path taken by the phaser with respect to the timing-chain cover can cause unacceptable leakage, or xe2x80x9ccross-talk,xe2x80x9d between the advance and retard passages, or loss of pressure sufficient to affect proper actuation of the phaser. Such eccentricities can occur easily because the phaser is centered on the camshaft by a pilot surface machined on the front end of the camshaft. Thus, because of machining tolerances, the phaser is not necessarily parallel to or coincident with the camshaft axis, once installed.
Further, it can be difficult or expensive to precisely locate the timing-chain cover relative to the camshaft-mounted phaser. Mounting the cover to the engine such that the bore in the cover is precisely concentric with the phaser can require expensive machining and manufacturing controls of the camshaft, the camshaft pilot surface, the phaser, and the timing-chain cover mounting features. Sealing an eccentric gap with resilient rotary seals can be unsatisfactory because of rapid wear of the seals or on aluminum wear surfaces in the cover.
Further, the timing-chain cover, being typically formed of aluminum alloy having a relatively large thermal coefficient, may expand more rapidly than the steel phaser, affecting the clearance and therefore quality of sealing therebetween.
A second problem exists in that many prior art cam phasers require extensive engine block and/or camshaft modifications to adapt the engine for use with the cam phaser, making their use more costly and less attractive to potential customers.
What is needed is a means for providing an effective seal between the timing-chain housing and the phaser rotor which can accommodate eccentric runout therebetween without seal wear.
What is further needed is a cam phaser requiring minimal or no engine modifications for adaptation to the cam phaser.
It is a principal object of the present invention to provide an improved means for rotary sealing a cam phaser to a timing-chain cover.
It is a further object of the invention to provide such means wherein the manufacturing tolerances of the components are readily met without undue expense or difficulty.
It is a still further object of the invention to provide a cam phaser requiring minimal engine modification for use with the cam phaser.
It is a still further object of the invention to provide a cam phaser requiring no rubbing seals against an aluminum alloy surface.
Briefly described, a rotary hydraulic seal assembly for sealing a rotationally eccentric annular space between a rotating cam phaser element and a stationary housing includes a generally cylindrical tubular sleeve disposable between the phaser element and the housing at the juncture of phaser-advance and phaser-retard control oil passages in the phaser element and the housing. The phaser element is typically a phaser rotor, although it may instead be a phaser stator. Radial bores through the sleeve allow oil to flow across the sleeve at the axial location of the passage junctures. The sleeve is provided with static seals disposed in grooves on the surface outboard of each juncture to prevent leakage between the junctures. The sleeve is rotatationally pinned loosely to either the phaser element or the stationary element. Because the sleeve does not rotate relative to its pinned partner, the static seals are not subjected to frictional wear. The surface of the sleeve opposite the static seal surface floats on a thin film of oil. The gap filled by the film of oil is thus annular with no eccentric runout, as the sleeve is hydraulically centered on the phaser; thus, cross-talk and leakage from the gap are minimized, and eccentricities between the timing-chain cover and the phaser element are radially absorbed by the static seals.